Structural Studies on Chick Embryonic Hemoglobins

Erythropoiesis in the chick involves the synthesis of multiple hemoglobins. The hemoglobins found in the late embryo and in the adult chicken are called hemoglobins A and D, and the hemoglobins found in the early chick embryo are called hemoglobins E, P, and M. We have determined the peptide chain composition of the embryonic hemoglobins E and P. During the chromatographic separation of hemoglobins E and P from the red cell lysate of a 5-day embryo, a previously unsuspected hemoglobin (M) was discovered which appears to be present also in 7-day embryos. Using rabbit antisera against hemoglobins A and D, it was found that hemoglobin E was very similar antigenically to A and that hemoglobins M and D were also related, although not as closely as hemoglobins E and A. Comparison of peptide maps of the S-aminoethylated globins of A, D, E, P, and M confirmed these relationships. Hemoglobin E appears to contain the αa chain of hemoglobin A, while the peptide map of the other (e) chain bears some resemblance to that of the β chain of adult hemoglobin A. An amino acid analysis of A globin and its individual chains and of E globin and its individual chains confirmed that the α chains of hemoglobins A and E are very similar, if not identical, while the e and β chains of these two hemoglobins differ. Hemoglobin P is composed of two closely related α-like chains, π and π', and a β-like chain, ρ. The ρ and the e chain share many common peptides on their peptide maps. Hemoglobin M contains the αd chain found in hemoglobin D, while the β-like chain of hemoglobin M resembles the e chain of hemoglobin E.